Wireless networks that have an infrastructure that includes a central station through which all other wireless stations communicate are now in common use for wireless data networks such as wireless local area networks (WLANs). Such infrastructure networks resemble cellular wireless networks that have a set of cells, the client stations within each communicating via a central station sometimes called a base station. The IEEE 802.11 standard in all its variations, for example, is now in common use for WLANs, and defines an infrastructure network having an access point (AP) through which all other stations (called client stations herein) of the same infrastructure network, also called a basic service set (BSS), communicate. It may be that several such BSSs exist in an area. A common approach to increasing capacity in a cellular network such as a cellular telephone network is to reuse the frequency bands as often as possible among cells in the network. However, this approach is not effective at increasing capacity in a wireless network such as one conforming to the IEEE 802.11 standard. For example, in a network conforming to one of the IEEE 802.11 OFDM variants, e.g., to the IEEE 802.11a or 802.11g standard, there can be a difference in receiver sensitivity of more than 15 dB between the highest data rate and lowest data rate. Therefore, if the region of coverage of a BSS (a “cell”) is sized such that typical performance at the boundary of the region of coverage of the BSS (the “cell boundary”) is at the highest data rate, then a signal transmitted at the lowest data rate can be received much farther away, and therefore might be a source of co-channel interference in a nearby cell.
According to the physical layer (PHY) parts of the IEEE 802.11 standard, a receiving station at the physical layer cannot differentiate between signals received from transmitters in its own cell versus transmitters in a neighboring co-channel cell. It is at the MAC layer that such a determination can occur. Thus, when a co-channel transmission is received, the receiver processes the signal until the end of the packet before the receiver MAC can determined whether or not the packet is intended for itself. So if the receiver is receiving an unintended co-channel signal, the medium is not available the entire time the receiver is processing the unintended co-channel signal. Much of the increase in spectral efficiency from frequency reuse may be lost due to such co-channel interference.
Thus there is a need in the art for a method and apparatus that can rapidly ascertain, e.g., at the physical layer whether or not a received packet is intended for the receiving station.